The invention relates to quantity flowmeters in general, and more particularly to improvements in apparatus for measuring fixed amounts of fluids in pulsating fluid streams. The invention also relates to improvements in methods of measuring fixed amounts of fluid in a pulsating fluid stream, e.g., a stream which is discharged by a metering pump.
It is already known to provide a quantity flowmeter with a swimmer or float which is movable back and forth in a conduit serving to convey a continuously flowing stream of fluid. As a rule, the float is biased (e.g., by gravity) counter to the direction of fluid flow in the conduit, and the float defines with the internal surface of the conduit an annular clearance for the flow of fluid around and beyond the float.
Determination of the volume of flow in a conduit for a pulsating fluid stream is often desirable, advantageous and necessary, e.g., to ascertain the quantity of fluid in each fluid pulse which is discharged by the outlet of a metering pump. A metering pump is often utilized to convey highly corrosive (aggressive), toxic or other fluids the flow of which must be regulated with a high degree of accuracy for the reasons of safety or for ecological reasons. Heretofore known quantity flowmeters which are used to ascertain the volume of flow of fluids in a steadily flowing fluid stream are not satisfactory for the measurement of fixed amounts of fluid in a pulsating fluid stream because their dynamics are insufficient and because they operate satisfactorily only when the flow of fluid in a stream is constant or varies gradually per unit of time.
A conventional quantity flowmeter normally employs an upright conduit wherein the float tends to descend under the action of gravity and wherein the inlet for the fluid stream is located at a level beneath the float, i.e., the fluid rises in the conduit and tends to entrain the float in the upward direction. It is also known to employ a spring which biases the float counter to the direction of fluid flow in the conduit. The float is often used as a limit switch to be actuated when the output of a pump which supplies the fluid stream drops below a preselected minimum value. A drawback of such flowmeters is that they can respond only under a single set of specific circumstances, namely when the output of the pump reaches a single preselected value. Such lack of versatility of conventional flowmeters prevents their use under many circumstances when a highly accurate determination of the volume of fluid flow is of considerable importance.
Other known proposals involve the utilization of magnetically inductive quantity flow measurements as well as ultrasonic and mass measurements on the basis of the Coriolis effect. In principle, such measurements could be utilized for determination of the volume of flow of fluid in pulsating fluid streams. However, the cost of a flowmeter whose operation is based on the Coriolis effect is very high. In addition, signals which are generated by such apparatus are not free of noise and, therefore, it is necessary to resort to noise suppressing circuits. A signal which has been caused to undergo noise suppression is not suitable for measurement of the quantity of fluid in short or very short fluid pulses.
Quantity flowmeters the operation of which is based on the positive displacement principle, turbine type counters and rotating impeller flowmeters are not suitable for measurement of the volume of flow in pulsating fluid streams because such streams cause rapid destruction of the flowmeters.
Swiss Pat. No. 673 893 to Barta et al. (granted Apr. 12, 1990) discloses a rotameter which is installed in a conduit for a continuous fluid stream, and an electronic circuit which includes an oscillator and a memory serving to store information pertaining to the position of the float in the conduit for the fluid stream.
UK patent application No. 2 202 331 A of Graham et al. (published Sep. 21, 1988) discloses an electromagnetic transducer wherein the conduit for a float is surrounded by a coil with turns in a stepped or tapered arrangement. The float is acted upon by a continuous stream of gaseous or hydraulic fluid.
European Pat. No. 0 063 405 to Inoue (published Aug. 26, 1987) discloses a fluid flow rate measuring apparatus wherein the diameter of the flow chamber in an upright conduit increases in an upward direction and the conduit is surrounded by a multi-turn single-layer electrical coil having an inter-turn pitch which progressively decreases from the lower end toward the upper end of the conduit. The measuring apparatus is designed to determine the rate of flow of fluid in a continuous fluid stream.
German patent application No. 32 29 788 of Romblom et al. (published Apr. 7, 1983) discloses an apparatus for ascertaining the quantity of fuel per stroke in a fuel injection system for combustion engines. The apparatus employs a plunger which is reciprocable in a pipe surrounded by a coil and receiving the plunger with a certain amount of clearance to permit the flow of fuel. The plunger is movable to a position in which it prevents the flow of fuel. The purpose of the apparatus is to ascertain the distance which is covered by the plunger in response to a fuel impulse because such distance is said to be indicative of the quantity of injected fuel.
German patent application No. 1 958 297 of Brunner (published Jul. 9, 1970) discloses a fluid flow meter which is analogous to that of Inoue.
Japanese patent application No. 60-236755 of Koike (published May 1, 1987) discloses a magnetic flux type flowmeter which tracks the position of a float in a liquid stream.
German patent application No. 38 33 678 of Hornung et al. (published Apr. 5, 1990) discloses an apparatus for measuring the flow of a viscous medium in a conduit. The apparatus employs a piston which is displaced against the opposition of a stressed coil spring. The volume of the viscous fluid which has passed through the conduit for the piston is determined on the basis of the extent of displacement of the piston from a starting position.